The present invention relates generally to shared communication systems, and, in particular, to the training of transmitters of such shared communication systems that are capable of near-continuous transmission of data.
Shared communication systems in which a communication resource, also known as a communication link, is used to support more than one type of communication service are known in the art. One example of such a shared communication system is the Time Division Multiplexed (TDM) communication system designed to support multiple services, such as voice communication services, circuit-switched data communication services, and packet-switched data communication services. In a TDM system, the communication resource is divided into a number of time portions of specified length, called time slots. A given communication service may then be assigned a specified portion of the available time slots, while other time slots may be assigned to other services.
Radio frequency (RF) transmitters are an integral part of shared communication units and systems, forming parts of subscriber units and base stations of shared communication systems, for instance. RF transmitters must be tested to ensure that proper, linear operation is maintained over changes in frequency, power, and transmission rate. In the present embodiment, so-called xe2x80x9cRF trainingxe2x80x9d of an RF transmitter, which includes phase and amplitude training, is thus performed regularly during a training interval of the transmitter to ensure that linear operation of the transmitter is maintained over changes in power, frequency, and temperature in the operating environment of the transmitter.
The advent of packet data in shared communication systems, such as the iDEN (integrated Digital Enhanced Network) communication system manufactured by Motorola, introduced the concept of dynamic channel allocation within a variable frame length. Time slots are dynamically allocated in response to constantly changing system requirements. The best allocation of the shared communication resource or link at any given moment in time is determined and then allocated according to the determination. Since demands on the communication resource are dynamic, the allocation of the resource between competing packet data communication services and devices is changeable over time as well.
Dynamic channel allocation has worked particularly well in TDM interleaved transmission modes, such as 3:1 and 6:1, for instance, in which data is transmitted every three slots or every six slots of a frame, respectively. Since data is only transmitted during a portion of the frame, there is plenty of time within the frame to perform RF training and then to process the results of the training to make any needed corrections to the RF transmitter prior to the next data transmission. With the need to transmit data in a near-continuous manner, such as in a 6:6 transmission mode in which data is transmitted every slot of a six-slot frame, however, the RF transmitter may transmit for an extended period of time in 6:6 mode without an opportunity to perform RF training. Since there is not enough time to process the training results of the previous slot before transmission occurs again, the result is degraded transmitter performance.
In addition to the concern with how near-continuous transmission by the RF transmitter affects RF training, there are other concerns with RF training. During the phase portion of RF training in which the amount of attenuation to use is determined, the RF power amplifier (RF PA) of the transmitter may saturate and cause RF interference, or xe2x80x9csplatter,xe2x80x9d on adjacent channels. Also, frequent RF training during every slot of the training interval can substantially drain the battery of a portable RF transmitter. These concerns point to a need in the art to be able to control when RF training of an RF transmitter is performed in a manner that overcomes the various shortcomings of the prior art.